The patch below does not apply to the 3.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 80b3ffce0196ea50068885d085ff981e4b8396f4 Mon Sep 17 00:00:00 2001

From: "Maciej W. Rozycki" macro@mips.com Date: Mon, 11 Dec 2017 22:53:14 +0000 Subject: [PATCH] MIPS: Consistently handle buffer counter with PTRACE_SETREGSET

Update commit d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") bug and consistently consume all data supplied to `fpr_set_msa' with the ptrace(2) PTRACE_SETREGSET request, such that a zero data buffer counter is returned where insufficient data has been given to fill a whole number of FP general registers.

In reality this is not going to happen, as the caller is supposed to only supply data covering a whole number of registers and it is verified in `ptrace_regset' and again asserted in `fpr_set', however structuring code such that the presence of trailing partial FP general register data causes `fpr_set_msa' to return with a non-zero data buffer counter makes it appear that this trailing data will be used if there are subsequent writes made to FP registers, which is going to be the case with the FCSR once the missing write to that register has been fixed.

Fixes: d614fd58a283 ("mips/ptrace: Preserve previous registers for short regset write") Signed-off-by: Maciej W. Rozycki macro@mips.com Cc: James Hogan james.hogan@mips.com Cc: Paul Burton Paul.Burton@mips.com Cc: Alex Smith alex@alex-smith.me.uk Cc: Dave Martin Dave.Martin@arm.com Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org # v4.11+ Patchwork: https://patchwork.linux-mips.org/patch/17927/ Signed-off-by: Ralf Baechle ralf@linux-mips.org

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c index 7fcadaaf330f..47a01d5f26ea 100644 --- a/arch/mips/kernel/ptrace.c +++ b/arch/mips/kernel/ptrace.c @@ -504,7 +504,7 @@ static int fpr_set_msa(struct task_struct *target, int err;

BUILD_BUG_ON(sizeof(fpr_val) != sizeof(elf_fpreg_t)); - for (i = 0; i < NUM_FPU_REGS && *count >= sizeof(elf_fpreg_t); i++) { + for (i = 0; i < NUM_FPU_REGS && *count > 0; i++) { err = user_regset_copyin(pos, count, kbuf, ubuf, &fpr_val, i * sizeof(elf_fpreg_t), (i + 1) * sizeof(elf_fpreg_t));